杭州地铁人民广场站深基坑降水研究

Research on Water Reduction Technology for Deep Foundation Pit of People's Square Station of Hangzhou Metro

研究目的：结合杭州地铁2^#线人民广场站深基坑降水的工程实践，采用三维渗流模型模拟基坑内外渗流场，选用有效的降水设计方案，保证基坑开挖期间安全，并对承压水降压风险和地面沉降进行分析，为类似工程积累宝贵的经验。研究结论：（1）降水工程的专业性强，地域性非常明显，类似工程经验非常重要；（2）钱塘江两岸分布着复杂深厚的第四纪松散沉积层，其间发育有多层厚度较大的孔隙承压含水层，各含水层之间发生强烈的水力联系，构成了一个复合含水层系统，具有极高的承压水位，大大加大了深基坑降水的难度；（3）在深基坑的降水设计中，必须将工程地质、水文地质条件和基坑的围护体系结合起来，选取合理的水文参数，进行详细的三维渗流分析，才能保证降水方案的合理、有效；（4）降水运行必须严格执行设计方案中的运行要求，尽可能减少承压水位降深，进而有效控制坑边路面沉降量，确保周围建筑物的安全；（5）实践证明，该方法正确、可靠，是复杂深厚第四纪松散沉积层地区承压水深基坑降水设计的良好手段。

Research purposes： Combined with the water reduction for the Peopleg Square Station of Line 2 of Hangzhou metro, a three - dimensional seepage model was used to simulate the seepage field inside and outside the deep foundation pit and the effective dewatering design scheme was adopted to ensure the safety of excavation of deep foundation pit. At the same time, the risk of dewatering for confined groundwater and the monitored data on subsidence were analyzed for providing the reference to the similar works. Research conclusions：As the water reduction engineering is strong in speciality and obvious in territoriality, the similar experience is very important. There are deeply complex Quaternary loose sediments distributed along Qiantang River, where multilayer thickness of pore confined aquifer is well developed. Strong hydraulic connection is dominated between aquifers, forming a complex aquifer system. Because high pressure water level is existence, it greatly increased the difficulty of dewatefing of deep foundation pit. In order to ensure rationality and validity of a dewatering design, the dewatering design must consider engineering geological conditions, hydraulic geological conditions and foundation bracing systems to select reasonable hydrological parameters and make analysis of seepage flow with three - dimensional seepage mode. The dewatering should be conducted strictly according to the dewatering design scheme with immediate dewatering and dynamic control to reduce the watering depth of pressure - bearing water for effective controlling the subsidence around the foundation pit as much as possible to ensure the safety of surrounding buildings. Proved by practice, the method is correct, reliable, and is a good mean to design the dewatering of deep foundation pit, where deeply complex Quaternary loose sediments exist.